Hydraulic hammers can be attached to various machines such as excavators, backhoes, tool carriers, or other like machines for the purpose of milling stone, concrete, and other construction materials. The hydraulic hammer is mounted to a boom of the machine and connected to a hydraulic system. High pressure fluid in the hydraulic system is supplied to the hammer to drive a reciprocating piston in contact with a work tool, which in turn causes the work tool to reciprocate while in contact with the construction material.
Typical hydraulic hammers drive the reciprocating piston to contact the work tool with the same continuous stroke. In other words, a stroke length of the reciprocating piston does not change during operation of the hammer. However, some hydraulic hammers are capable of changing the stroke length (e.g., between shorter and longer strokes), which can provide more efficiency in some hammer operations.
An exemplary system for changing the stroke length of a hydraulic hammer is disclosed in U.S. Pat. No. 5,669,281 (the '281 patent) that issued to Comarmond on Sep. 23, 1997. Specifically, the '281 patent discloses a percussive machine having a piston that slides in a cylinder and strikes a tool during each cycle. The percussive machine also has a top chamber and a bottom chamber which are fed sequentially with fluid through a distributor controlled by a control device. The percussive machine further includes a selector piston mounted in the cylinder. The selector piston may be controlled by the control device with pressurized fluid to shift the selector piston in and out of a position that lengthens the stroke of the piston.
Although the percussive machine of the '281 patent may be adequate for some applications, it may still be less than optimal. In particular, the percussive machine of the '281 patent may be overly complex and require many additional parts. As a result, retrofitting existing hydraulic hammers with one continuous stroke to have an adjustable stroke would be difficult to achieve with the percussive machine of the '281 patent. In addition, the percussive machine of the '281 patent operates initially in a short stroke mode and is later switched to long stroke mode after a period of operation. In some instances, however, it may be desirable to start in the long stroke mode initially to increase the efficiency of the hammer operation.
The disclosed system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.